1. Field of the Invention
This invention relates to plastic closures for containers and particularly to such closures having a barrier layer embedded in the plastic.
2. Background Information
Many food products are placed in containers and sealed by a closure while the product is still at a temperature which will kill bacteria. As the product cools, it is common for a vacuum to be created inside the sealed container. If plastic closures are used which are not gas impermeable, air can be drawn into the container which contaminates the product if it is oxygen or a nitrogen sensitive. In addition, even products which are not hot filled can be contaminated by air or water vapor if the closure is not gas impermeable. In addition to food products, this can include pharmaceuticals, for instance. There are also products such as carbonated beverages and products incorporating solvents such as paint or other aggressive chemical products such as insecticides and herbicides in which it is deleterious to have gases or vapors permeate through the plastic closure. There is also a need to prevent the deterioration of aromatic products such as cosmetics through plastic closures which do not block transmission of the vapors.
It is common to include a separate liner within a plastic closure. It is also known to provide seals over a container opening. However, the latter only protects the product prior to the initial opening of the container and removal of the seal.
There is a need, therefore, for improvement in molded plastic closures for hot fill products, gas sensitive products and vapor gas-producing products.